1. Field of the Invention
The present invention relates to an adjustable dial gauge adaptor for the firm placing and fine setting of dial gauges. Dial gauges are primarily used for the measurement of precision mechanical constructions.
2. Description of Prior Art
Dial gauges are equipped with a moveable sensing lever. A sensitive, highly precise mechanical movement converts the displacement of the tip of the sensing lever into a value displayed on a dial or a digital display. The spherical tip of the sensing lever forms the contact point with respect to the object being measured. This tip must be brought into measuring position with very close tolerances and be held in place very firmly. The dial gauge is usually fastened to an articulated stand which allows a first, approximative positioning. Once it is positioned, the articulated stand can be locked, thus firmly holding the dial gauge in a position relatively close to the chosen reference point.
The dial is graduated in a positive and a negative direction from a zero setting. Before a measurement is made, the dial must be set to zero. This is done by a fine adjustment of a dial gauge adaptor. This adaptor is fastened to the tip of the articulated stand and holds the dial gauge in place. The purpose of the adaptor is to hold the dial gauge and to position it more precisely after the articulated stand is fixed, in order to set the dial to zero before proceeding with the measurement.
Conventional dial gauge adaptors have of two separate pieces forming two legs connected by a pin at a common axis. The legs are held in position with a tensed spring and their relative position can be changed with a fine adjustment screw. The one leg is firmly connected to the tip of the stand while the leg other can be moved relative to the first by adjustment of the fine adjustment screw which works against the force of the tensed spring. The dial gauge is fastened to this second leg of the adaptor and can thus be moved precisely into position.
The disadvantage of these conventional dial gauge adaptors is that a slight play results from the two-piece construction. This is evidenced by a hysteresis in the position of the dial gauge when it is moved back and forth. This play, especially in the lateral direction, occurs despite the most rigorous tolerances in the construction of the adaptor. Furthermore, a minimal play in the construction is necessary to prevent the two legs from getting jammed. In that case, a fine adjustment would be impossible, since the spring would not be able to overcome the resistance to movement of the joint.
The fine adjustment screw of the adaptor passes through the one leg and its rounded tip bears on the inner side of the other leg. In order to optimize the force ratios in the two-piece adaptor, the fine adjustment screw must be placed farthest away from the end at which the two legs are joined by the pin. The resulting large leverage allows a very fine adjustment and setting of the adaptor. This requirement, of placing the fine adjustment screw as far as possible from the joint, leads to relatively large dimensions for the legs of the adaptor and to a correspondingly reduced stability.
One dial gauge design is known, in which the legs form a single, shaped part. The part is thinner at the base of the legs, where they are joined. Thus the elasticity of the material can be used to act as a combination of the axis and the spring. The two legs first run parallel to each other, up to shortly before the end of the shorter leg. At that point, the longer leg forms a fight angle and continues, over a length equal to that of the shorter leg, in a direction perpendicular to the shorter leg and away from it. This longer leg has a smooth face at the tip where it forms a right angle. A fine adjustment screw bears on this face in the unloaded position of the adaptor, when the legs are relatively close to each other. The fine adjustment screw passes through the the tip of the shorter leg at an angle of 45.degree. to it. The base of the adaptor, where its two legs join, is fastened to the stand and the dial gauge is attached to the tip of the longer, angled leg of the adaptor.
Two disadvantages of the aforementioned design must be pointed out. First, the conical tip of the fine adjustment screw bears excentrically on a conical depression in the flat face of the longer leg at the beginning of its range of motion. As the two legs are moved apart, the tip of the fine adjustment screw moves along the side of the conical depression, toward its center. This is associated with large frictional forces at the contact point and considerable lateral forces on the leg being displaced by the setting of the adjustment screw. The resulting load on the screw leads to wear of the screw threads and consequently to an increased play in the movement. Secondly, the two legs form an equilateral triangle with their base. As a result, when the horizontally mounted adaptor is adjusted, the tip of the dial gauge moves not only up and down, but also forward, toward the object being measured. This causes a displacement of the dial gauge tip relative to the reference point on the object, and presents some difficulties for the exact positioning of the gauge.